1. Field of the Invention
The present invention relates to an improvement for obtaining a semiconductor power module resistant to electric noises.
2. Description of Background Arts
In a semiconductor power module, a combination of a main circuit and a control circuit are provided in the form of a single device, in which the main circuit comprises a semiconductor clement for controlling electric power while the control circuit comprises another semiconductor element for controlling the operation of the main circuit. Such a semiconductor module is often utilized in an inverter for controlling motors, and the like. The semiconductor power module should be capable of switching a power at a high frequency to reduce the power loss and to ensure a quick response and an accuracy in the objective device to be controlled by the semiconductor power module, e.g, motors. Further, it is desired to obtain semiconductor power modules operable to control higher power and usable for driving large-size motors of industrial use. In response to this demand, new semiconductor power modules have been developed, in which an insulated gate bipolar transistor (which will be hereinafter referred to as "IGBT") capable of high-speed switching is used as a power control semiconductor device so that a voltage of about 220 V and a current of about 30 A are controlled at a frequency of about 10 kHz.
However, it is still required to obtain devices capable of controlling higher power at higher frequency. The following problems should be solved in order to obtain semiconductor power modules operable to control a voltage of about 440 V and a current of 30 A through 600 A at a frequency of 10 kHz through 20 kHz.
In general, electric noises increase in proportion to the operation frequency and the current to be controlled. The electric noises often cause operation errors in the semiconductor elements included in the control circuit. Accordingly, even if the design of the power semiconductor modules is changed such that power semiconductor elements of high-speed switching and large current capacity are mounted on circuit boards of large current capacity, it is impossible to prevent operation errors due to electric noises to obtain semiconductor power modules of higher frequency and larger current.
Also in lower power modules for an output voltage of 220 V and an output current of at most 30 A, for example, it has been desired to prevent operation errors due to electric noises to reduce the size of the modules.